Proposal Information for 2007B-0414

Abstract: A determination of the Hubble constant to better than 5% is required to improve upon the current constraints on the equation of state of dark energy. An essential step towards that goal is the accurate and precise calibration of the near-infrared Cepheid P-L relation, and an improved measurement of the "metallicity dependence" of the Cepheid Distance Scale. We have obtained deep JHK_s photometry of Cepheids in M33 with Gemini/NIRI, which resulted in the largest and most complete sample of Cepheids in any galaxy at these wavelengths. We propose to obtain a very precise and accurate calibration of the Gemini photometry into the all-sky 2MASS photometric system using FLAMINGOS at the KPNO 4-m with a very modest investment of telescope time. Once properly calibrated, the Gemini data will be combined with existing WIYN optical observations to derive the metallicity dependence of the Cepheid Distance Scale from B to K_s and test for any variations in P-L slope as a function of abundance.